Diffuse knapweed grows in a variety of habitats in washington including river shores, rangeland and pastures. These two species of insects are nearly indistinguishable. In larimer county, its found mostly in the southeast part of the county, estes park, red feather lakes, pinewood springs and u. Insects that eat spotted knapweed weedbusters biocontrol.
The plant has a white flower, grows to a height of 24 inches, and has a short taproot. Effect of biocontrol insects on diffuse knapweed centaurea. What to do if you find this plant in king county, washington. The enemy diffuse knapweed centaurea diffusa this annual and sometimes biennial noxious weed is a native of eurasia and spread into the u. Two cytotypes of the plant exist which have been named as either different species or subspecies. This book was published by fhtet as part of the technology transfer series.
In seasonally dry areas, spotted knapweed s taproot allows it to access water from deep in the soil, beyond the reach of more shallowly rooted species. White knapweed, spreading knapweed, tumble knapweed distribution in oregon. This tap rooted member of the aster family is native to southeastern europe. There is some evidence that they release chemical substances which inhibit surrounding vegetation. Diffuse is a member of a large genus of over 400 species, most originating in the mediterranean region. United states department of agriculture natural resources. I think that this knapweed spread very quickly in the years of 19751999. Diffuse knapweed is a biennial to shortlived perennial that reproduces by seed. Publication date 1994 topics knapweeds biological control united states, diffuse knapweed biological control united states. Background spotted knapweed was introduced to north america from eurasia as a contaminant in.
U of i idahos noxious weeds control guidelines 183 kb pdf download other resources. Diffuse knapweed north dakota department of agriculture. Cultivation is effective when repeated, but diffuse knapweed typically grows in areas not conducive to. A weed report from the book weed control in natural areas in the western united states diffuse knapweed. All knapweeds are highly competitive herbs and can form dense colonies in disturbed or overgrazed lands. For more information, click on the link below to download the idahos noxious weeds control guidelines publication produced by the university of idaho extension. Spotted knapweed is native to eastern europe, with a locally scarce but widespread distribution. Biological control of spotted and diffuse knapweeds computer. Diffuse knapweed can be confused with nonnative spotted and russian knapweeds, both of which need to be eradicated. Institute of arctic and alpine research, and department of environmental, population and organismic biology, university of. Because diffuse knapweed is an obligate outcrosser, seed production can be greatly reduced when diffuse knapweed is mowed prior to flowering.
Diffuse knapweed centaurea diffusa best management practices including impacts, history, habitat, description, reproduction, manual control, mechanical control, biological control, chemical control and best management pracoa ax kom. Its basal leaves leaves at the stem base have short stalks and grow 7 to 8 inches long. Several of these are well established in colorado and are probably having an impact on the knapweeds. This larval feeding reduces knapweed density and can result in death of small plants. Biological control of spotted and diffuse knapweeds computer file by delfosse, ernest s. Diffuse knapweed is native to grasslands and shrub steppes of the eastern mediterranean and western asia. Spotted knapweed was formerly or incorrectly known as centaurea biebersteinii and centaurea maculosa. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm in height.
It also thrives in disturbed habitats such as gravel pits, roadsides, railroad tracks, vacant lots, airports, trails and heavily grazed pasture. The single upright stem grows 15 to 60 cm in height and has numerous branches mostly on the. Close mowing at the bud or flowering stage can reduce infestation june to october but flowering stems may regrow. The colorado department of agriculture has released a number of biocontrol agents against diffuse and spotted knapweed including a two root boring beetles, two seed head feeding flies, seed head feeding weevils and seed head feeding moths. Invasive plant atlas of the united states diffuse knapweed. Diffuse knapweed cannot tolerate cultivation or excessive moisture and.
Hand dig or pull the rosette during their first year of growth. Spotted centaurea biebersteinii and diffuse knapweed centaurea diffusa are biennial to shortlived perennials, and considered regionally noxious under the bc weed control act. Diffuse knapweed was probably introduced accidentally in alfalfa seed. This plant produces chemicals that inhibit growth of surrounding plants. It is often found in open, disturbed areas where it grows in tufted clumps. It is a perennial, polycarpic plant, meaning that it lives and flowers for several years, produces more than one. Seastedt et al reduction in diffuse knapweed by insects x 237 weed science, 51. Diffuse knapweed infestations can greatly reduce dryland forage production with estimated losses of up to 88% in some areas of the united states. Not listed on any labels except for diffuse knapweed on the banvel label. The decline of diffuse knapweed in british columbia. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres.
Diffuse knapweed is a nonnative biennial forb that reproduces solely by seed. Yellow starthistle is another less robust annual type. Diffuse knapweed identification and management diffuse knapweed. Overall, knapweeds are a large group of over 400 species, many of which are considered invasive weeds. Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar.
A biennial is a plant that completes its life cycle within two years. These weeds are well adapted to a wide range of habitats including open forests, rangeland, roadsides, pastureland, riparian areas, and ditch banks. The knapweeds were added to the nebraska noxious weed list in 1992 because of their potential threat to the economic, social, and aesthetic wellbeing of rangelands and. Cyphocleonus achates, or the knapweed root weevil, is a robust biological control agent that can attack spotted preferred host and diffuse knapweeds. Diffuse and spotted knapweed biocontrol department of. Russian knapweed is the most difficult to handle, since this perennial knapweed digs in for the long haul it can set roots as deep as 20 feet below the surface of the soil. Diffuse knapweed is a bushy, taprooted bienniel or shortlived perennial. Diffuse knapweed centaurea diffusa, also known as white knapweed, is a member of the genus centaurea in the family asteraceae. Diffuse knapweed national invasive species information center. Shallow cultivation is not effective but deep plowing 18 cm followed by vigorous establishment of grasses can reduce the infestation. Diffuse knapweed is generally a shortlived perennial or biennial in north dakota and invades habitats similar to spotted knapweed.
Please consult the plants web site and your state department of natural. Diffuse knapweed floral bracts have yellow spines with teeth appearing as a comb and a distrinct terminal spinte. The colorado department of agriculture currently releases this agent as the primary biocontrol for diffuse knapweed. Mowing diffuse knapweed in british columbia at the bud stage and again at flowering reduced the number of plants producing seed by 77 to 99% compared to unmowed plants. Washington state noxious weed control board external link diffuse knapweed best management practices 204 kb acrobat file selected knapweeds of washington 316 kb acrobat file.
Pdf the decline of diffuse knapweed in british columbia. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and regrow. Spotted knapweed is a biennial or shortlived perennial. Spotted knapweed tolerates a wide range of temperature and moisture conditions, and is well adapted to openforest, pastures, and crp land in wisconsin. Both knapweeds spread in alfalfa seed and hay before they were considered problem weeds. Spotted knapweed and diffuse knapweed are closely related noxious weeds infesting over 7 million acres in 17 western states duncan and jachetta 2005. Diffuse knapweed, is a biennial or shortlived peren. Some other interesting things are its effects against fire.
Robust, bushy plant, generally shorter than spotted knapweed. Diffuse knapweed identification and management diffuse. Burning has been shown to give effective control of diffuse knapweed while stimulating grass regrowth. It is native to asia minor turkey, syria, the balkans, bulgaria, greece, romania, ukraine, and southern russia. Spotted knapweed typically forms a basal rosette of leaves in its first year and flowers in. The most prevalent of the five knapweed species in ontario is spotted knapweed. When a diffuse knapweed plant has been cut, the rosette may live and rebolt. Currently distributed throughout southern bc, both spotted and diffuse knapweed are a. It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. Additionally, diffuse knapweed seeds can remain dormant for several years, requiring any cutting program to be repeated several times annually spring, summer, and fall to be effective. It produces toxic chemicals that can inhibit the growth of desired plants and is a highly competitive plant. The beetle feeds on the seed heads but is also a foliage feeder as an adult. However both species of weevils feed readily on both species of knapweed.
Hi entomologists and permies, we have a little knapweed problem, spreading up the road from plum creek lands into our native montane grassland at 6000 along our roadoops. Adult and pupa taken from the root of the plant that provided the spotted knapweed flower. Ecology and management of diffuse knapweed centaurea diffusa lam. Knapweeds readily establish themselves on any disturbed soil, and their early spring growth makes them competitive with other plants for moisture and nutrients. Spotted knapweed integrated pest and crop management. Largescale control against diffuse knapweed has been seen at a number of locations along the front range. One plant can give rise to 1 to 20 slender, upright stems 24 feet in height with most branching occurring in the upper half. Biological control of spotted and diffuse knapweeds computer file by delfosse. Spotted knapweed is found at elevations up to and over 10,000 feet and in precipitation zones receiving 8 to 80 inches of.
King county best management practices for diffuse knapweed. During the first year of growth, diffuse knapweed appears as a rosette in spring or fall. This plant may be known by one or more common names in different places, and some are listed above. Spotted knapweed is distinguished from the closely related species, diffuse knapweed c. Pdf sustainable control of spotted knapweed centaurea stoebe. Sustainable control of spotted knapweed centaurea stoebe. Plants profile for centaurea diffusa diffuse knapweed. Diffuse knapweed was found in one north dakota county in 1996 and infested approximately 20 acres. This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Biological control of spotted and diffuse knapweeds. Disturb the soil as little as possible, to reduce germination of new seedlings.
Dense infestations of spotted and diffuse knapweed can reduce productivity of grazing lands and wildlife habitat and increase. There arent any biocontrol agents that far up in the mountains, and im trying to get populations of two weevils started root weevils and flower weevils. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. Diffuse knapweed survives in a wide range of soil and environmental conditions, and produces large numbers.
Top of page diffuse knapweed is native to grasslands of western asia and southeastern europe. It grows from 8 to 40 inches tall, with branching stems covered in short, dense hairs and a very long tap root. Distribution, biology, and management of diffuse knapweed centaurea diffusa and spotted knapweed centaurea maculosa. However, mowing at the late bud to early bloom stage will reduce seed production. Centaurea diffusa wikibooks, open books for an open world. These knapweed varieties are generally unpalatable to livestock, and spines on the flower heads of diffuse knapweed may cause injury to the mouth and digestive tract of grazing animals. Diffuse knapweed is a shortlived perennial or sometimes biennial plant reproducing solely by seed. Knapweed removal information how to get rid of knapweed. Spotted knapweed centaurea stoebe 1 introduction spotted knapweed centaurea stoebe is a plant belonging to the sunflower asteraceae family. Pca alien plant working group spotted knapweed centaurea. Highway 287 north of fort collins to the wyoming border. Diffuse knapweed was brought in from europe mediterranean region. Members of this trio include spotted, diffuse, and russian knapweed.
University of nebraskalincoln extension ec173 revised. These weeds are well adapted to a wide range of habitats including open forests, rangeland, roadsides, pastureland, riparian. Spotted knapweed and diffuse knapweed are both shortlived perennials that sometimes behave like annuals. Usda national invasive species information center diffuse. Mowing or chopping is most effective when diffuse knapweed plants are at fullbloom. The plant is one of over a dozen centaurea species that were accidentally introduced into. Diffuse knapweed survives most low burning and medium fires. A weed report from the book weed control in natural areas in the western united states spotted knapweed. The seeds can germinate from spring through early fall. A winterhardy biennial or short lived perennial with a taproot.
Although widely, diffuse knapweed has limited distribution in oregon with the northeastern and central areas having the heaviest infestation. Ecology and management of diffuse knapweed centaurea diffusa. The common name spotted knapweed most often refers to centaurea maculosa. This plant may be known by one or more common names in. Diffuse knapweed centaurea diffusa quick identification. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states. Po box 315, twin bridges, mt 59754 406 6845590 888 6644153 fax becky l. Diffuse knapweed is found across colorado, primarily along the front range and east to limon. See separate pages on these invasive plants on this website. Distribution, biology, and management of diffuse knapweed. Larval feeding in the seedhead destroys the knapweed seed before it matures. Emergence date effects on resource partitioning between diffuse knapweed seedlings. Spotted knapweed is one of 3 targeted plant species in minnesota with an active biocontrol program, the other 2 species are leafy spurge and purple loosestrife.
Diffuse knapweed department of agriculture conservation. Spotted knapweed does not compete well with vigorously growing grass in moist areas. Diffuse knapweed cannot tolerate cultivation or excessive moisture and is therefore uncommon on cultivated land. Spotted and diffuse knapweed reduce productivity of grazing lands and wildlife habitat and increase. Centaurea diffusa, also known as diffuse knapweed, white knapweed or tumble knapweed, is a member of the genus centaurea in the family asteraceae. Within 2 years of burning, most diffuse knapweed rosettes were eliminated. A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a severe fire can kill some of the plant crowns. Minutus prefers diffuse knapweed while obtusus prefers spotted knapweed. Executive office montana weed control association, inc.
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